A constitutional amendment that would ban gay marriage has won the endorsement of a key Senate committee in Indiana.

Indiana law already prohibits gay marriage, but opponents worry gay activists could challenge the law in the courts.

The Senate Judiciary Committee voted in favor of sending Republican Senator Carlin Yoder's amendment to the full Senate in a 6 to 4 vote. Democrats mostly voted against the measure.

“The Marriage Discrimination Amendment violates every Hoosier's basic right to fairness and equality,” Randy Studt, president of the gay rights group Indiana Equality, said in a statement. “It's just an attempt to distract Hoosiers from the greater issues facing Indiana, threatening our state's current and future economic development.”

The measure seeks to ban civil unions for gay couples as well as marriage. Both chambers of the Assembly need to approve the resolution twice before voters can weigh in on the issue.

James Bopp, a prominent anti-gay lawyer and Terre Haute resident, helped draft the amendment. Bopp is involved in several high-profile cases involving gay rights, including a California lawsuit aimed at shielding the identities of donors to anti-gay campaigns.

Lawmakers in nearby Ohio and Michigan have proposed legislation that would repeal their gay marriage bans.